1. Field of the Invention
The invention relates generally to insulated conducting wires (ICW) having a gap between a microwire and a cladding, and processes for making the same.
2. Description of the Prior Art
The Taylor process is a method of a making a very fine wire, referred to as a microwire. The microwire is encased in a cladding. The process is described in Donald et al., “The preparation, properties and applications of some glass-coated metal filaments prepared by the Taylor-wire process,” J Mat. Sci., 31, 1139 (1996). The metal to be made into a microwire is contained in a glass tube which is closed at one end. The metal is then melted and the end of the glass tube softened and drawn down to produce a fine glass-encapsulated metal filament. A limitation of this method is that the metal microwire is in contact with the glass. This prevents the wire from being useful at high temperatures because the metal can diffuse into the glass, reducing the insulating, electrical, and mechanical properties of the glass. A further limitation is that the glass must be drawn at above the melting point of the metal.
There are known inorganic cladded metal wires which are capable of conducting electricity under high voltages and high temperatures such as 1000 V and 500° C. For example, a Pyrex coated stainless steel wire, typically used in photocopy machines. Another example is a glass coated gold wire that can be made as small as 600 nm in diameter. However, such wires are not flexible and tend to be brittle, primarily due to the insulating coating. They cannot be fabricated in long lengths either. Flexibility is a required characteristic for certain applications such as decoy towlines. The best flexible ICW is able to perform up to only 400° C. and contains a flexible organic insulating coating which decomposes over time at high temperatures. An example of such an ICW is a copper wire coated with polyimide.
There remains a need for a flexible wire at least 30 centimeters in length that is capable of conducting at 1000 V and 500° C.